The proposed research activity continues an effort to define the functional relationships that occur between the reception of light, the routing of coded information to neural centers, and the expression of that information in visual behavior. The research effort employs techniques of behavioral conditioning, electrophysiology, and absorption spectroscopy to define reactions of the organism to light. The present proposal correlates visual pigments uncovered by microspectrophotometry with single unit electrical changes in the visual system induced by parameters of light stimuli. The neural responses to light are then correlated with behavioral data for appropriate threshold functions. The work is to be accomplished on two species of turtle, Pseudemys scripta and Chelonia mydas, and on the pigeon, Columba livia. These animals have cone-dominated vision and these structures are instrumental in color discrimination and information processing.